In connection with surgery for a number of diseases in the gastrointestinal tract a consequence is, in many cases, that the patient is left with an abdominal stoma such as a colostomy, an ileostomy or an urostomy in the abdominal wall for the discharge of visceral contents. The discharge of viseral contents including intestinal gases cannot be regulated at will, and for that purpose the intestinal opening may be closed with a closure means, e.g. a tampon or a magnetic closure, or the patient will have to rely on an appliance to collect the material emerging from such opening in a bag which is later emptied and/or discarded at suitable times.
The discharge of flatus, measured in volume, may exceed the discharge of solid and liquid faecal matter by many hundred percent and therefore there is usually the need for the continuous or frequent venting of the intestine or the collecting bag. Normally the outflowing flatus is deodorised with a suitable filter. Commonly the active filter is powdered active carbon, which absorbs H.sub.2 S being the principal component of the smell of flatus.
Various constructions of filters for ostomy appliances are known. In the state of the art, the filters are designed so as to obtain a high security of deodorisation of the flatus by insuring that there is no by-pass by which the flatus may circumvent the filter, and some measures have been discussed with respect to obtaining a better security against blocking of the inlet of the filter by solid discharged visceral content. When the inlet opening of the filter is blocked, the gas discharged into the ostomy appliance will lead to ballooning of the bag which is highly undesirable for several reasons. Ballooning will be embarrassing for the user as the bag will bulge and there is an increased risk of leakage which is unacceptable for the user. Another problem may arise when applying a fresh ostomy appliance as a vacuum in the bag may give a "pancaking" effect, i.e., the front wall and the rear wall stick together and are very difficult to separate which may hamper the discharge of visceral contents into the bag.
Examples of filters are described in U.S. Pat. Nos. 3,804,091, 3,952,727 and 3,759,260 wherein activated carbon particles are present in a filter body of matted fibres and wherein the filter body is arranged such that the flatus passes therethrough in various ways. However, it is a drawback of the filters known from these specifications that there is no firm surface connection between the filter body and the plastic, gas impermeable cover sheets therefor whereby a flow of gases may occur through the filter without passing through the filter body and hence without being deodorised. This for instance may take place as a result of bending or bowing the filter consequent e.g. upon the patient bending, which can cause small interspaces or channels to be formed between the filter body and one of the walls.
U.S. Pat. No. 4,490,145 discloses an ostomy pouch with a deodorising filter. The filter consists of a filter element affixed to the outside or inside of the pouch outer wall and comprising a polymeric film cover attached to the said pouch wall, and an insert of a gas deodorising material, e.g. of one of the kinds mentioned above. The pouch wall has an aperture providing entry to the filter element and the polymeric film cover has an aperture for venting the deodorised gas to the atmosphere. The two apertures are spaced from each other in order to let the intestinal gas pass through the length of the insert of deodorising material. U.S. Pat. No. 4,490,145 does not disclose a positive sealing connection between the film cover for the filter element and the insert of deodorising material but in a commercial ostomy pouch, "ConvaTex" made in accordance with this U.S. patent one surface of the deodorising material is sealed to the outer pouch wall whereas the opposite surface of the deodorising material is not sealed to the polymeric film cover; accordingly there is a space between the deodorising material and the cover through which gas can flow freely, especially in cases of bending of the filter. This means that the intestinal gas can pass directly across the thickness of the deodorising material, i.e. about 1 or 2 mm, and then through the space defined between such material and the polymeric film cover. Satisfactory deodorising cannot therefore be achieved.
A similar filter construction is disclosed in DE Utility Model No. 7525408 in which the filter element comprises a filter housing with apertures for the inlet and outlet of gases and containing an odour absorbing material. The latter may be connected with one side of the filter housing and the two apertures are spaced as far from each other as possible. Again, since only one side of the absorbing material is connected to a wall of the housing, the gas may pass between that wall and the absorbing material and may thus only be subjected to deodorising as a result of passing directly through the thickness of the absorbing material.
These drawbacks have been overcome by the filters described in GB 1,571,382 and EP 0089,110 in the name of Coloplast A/S, wherein a plastic wall has been glued or hot sealed to a filter body consisting of an open cell foam plastic impregnated with the activated carbon particles. These filters preferably are formed as circular discs of a thickness of 2-3 mm and a diameter of 25-30 mm and having an aperture in the centre of the filter material and in one of the walls arranged such that the flatus enters through the aperture in the wall and flows into the filter material through the edges of the aperture therein, and flows radially through the filter and leaves it through its cylindrical outer edge.
These filters function well and are particularly suitable for ostomy bags. They are adapted to yield a small gas resistance within the filter material and hence a low drop of pressure, and the same is true for the arrangements known from the US specifications discussed above. The purpose of the low drop of pressure is to ensure that the bag does not inflate and thereby become visible on the outside of the wearer's clothing, which should be avoided for obvious reasons. If, however, the drop of pressure becomes too low this can also create problems. Firstly it can occur that the entire volume of gas in the bag escapes so that the walls of the bag, consisting of a smooth plastic sheet material, stick together and also stick to the ostomy. This prevents faeces from the ostomy from falling to the bottom of the bag, and may also increase the risk of clogging the venting hole or holes in the wall of the bag. Sooner or later this can result in unacceptable bulging of the bag.
Secondly, a too high flow velocity through the filter may result in inefficient deodorising of the intestinal gases flowing out through the filter. The problem of avoiding a sudden fall of gas pressure in the interior of the pouch has also been taken into account in the above-mentioned U.S. Pat. No. 4,490,145 in which it is proposed, in order to keep the gas deodorising material dry and control the rate at which gas can pass from the pouch into the filtering element, to cover the inlet and/or outlet aperture by a barrier layer of a gas permeable, liquid impermeable material. However, such barrier layers will not only create a certain distension of the pouch itself, but also tend to cause distension between the insert of gas deodorising material and the surface thereof not sealed to the pouch wall and hence promote the above-mentioned tendency for the gas to travel through only the thickness of the insert and not along its length. This in turn will promote a fall of gas pressure in the interior of the pouch.
European patent No. 0 235 928 discloses a filter for ostomy bags and the like in which a higher drop of pressure occurs therein than in known filters, but wherein the drop of pressure is not so great as to cause over inflation of the bag offering a solution how to overcome the drawbacks of known arrangements mentioned above and to provide venting for ostomy bags and the like. The drop of pressure being higher than in known filters ensures that the bag is maintained inflated to a suitable degree by the intestinal gas which flows in more or less continuously so that wall of the bag opposite the filter does not stick to the opposite wall giving rise to an build up of pressure which will be unmistakable on the outside of the patient's clothing, which for psychological reasons clearly should be avoided but not be so big such that high inflation of the bag occurs in any case.
European Patent No. 0 235 928 further discloses that a filter may be rendered suitable for use with ileostomy equipment when the filter wall adapted to face the source of intestinal gas is covered by a layer of sheet material, preferably plastic sheet material connected to the filter walls and inside the periphery of this connection, provided with openings for the passage of intestinal gas. Conveniently these openings, which may for instance be slits of a width of 0.5-1 mm and a length of a few millimeters, may be situated outside the peripheral edge of the filter body. However, such slits may open if the pressure is high giving free flow of gas and liquid through the layer of sheet material. In the alternative, it is proposed to provide the filter housing on the surface adapted to face the source of intestinal gas with a layer of liquid-absorbing material. The area of the absorbent material is conveniently the same as the area of the filter body or somewhat larger but the positioning on the wall in question should be such that the absorbent material does not cover the inlet opening for intestinal gas to be deodorised since saturation of the liquid-absorbing material with liquid might prevent the passage of the intestinal gas. Furthermore, it is proposed to render the filter particularly efficient for ileostomy equipment by providing it both with a covering sheet and an absorbent layer of material.
EP patent No. 0 443 728 B1 discloses a bag for receiving discharge from the human body comprising a filter and an intervening membrane covering the inlet opening of the filter, said intervening membrane being gas permeable but not liquid permeable. It is mentioned that the membrane may comprise a polyester film bonded to a PTFE film and that such membrane showed no leakage of water. There is no indication of security against leaking when exposed for discharge from an ileostomy or liquids from a colostomy.
British patent No. 1 571 382 discloses collection bag having a venting device situated between the skin of the patient and the collection bag surrounding the inlet opening of the collection bag which venting device may have an inner ring of a gas-permeable hydrophobic material or of an open-celled hydrophobic foam plastics material. This reference does not offer a solution to the problems mentioned above.
GB 2 259 255 discloses a medico-surgical collection bag for body waste products comprising a front wall and a rear wall of flexible material. The rear wall has an opening into the bag by which waste material can enter the bag and one of the walls has vents and a seal for the vent such that when the seal is open, the front wall can be pulled away from the rear wall and then air is drawn through the vents and is trapped within the bag. The air trapped in the bag when closing the vent keeps the front wall away from the rear wall in the region of the inlet opening. This measure, however, only provides a solution to the second problem, the "pancaking", and is only effective when the opening of the vent is closed and does not prevent blocking of the inlet of the filter by solid discharged visceral content of the bag.
U.S. Pat. No. 5,549,587 discloses an ostomy bag having a liquid-gas separating device made of an absorbent material to collect liquids. Such a solution may overcome the problem of "pancaking". However, there is not a restricted access to the inlet opening of the filter and there is no teaching of a direct protection of the inlet opening of the filter against clogging.
U.S. Pat. No. 5,342,434 discloses a gas permeable coated porous membrane having enhanced oleophobic and hydrophobic properties. The membrane may be a PTFE membrane coated with a diisocyanate coating and the membranes are stated to be useful in waterproof, breathable fabrics and gas vents or filters that protect electronic equipment used in or near automotive engines. Other useful applications are stated to be medical devices where venting filters are needed and in industrial filtration where venting filters are needed, where oil mists are present. It is even stated that the coated products are useful as filters in medical vents where oil or fatty substances in parental drip bottles can clog gas vents. However, this reference is silent with respect to safety against wetting of filters for ostomy appliances by the visceral contents of an ostomy collection bag which contents has a very complex composition of biologically active compounds fro the digestive system.
U.S. Pat. No. 4,490,145 discloses an ostomy appliance comprising a front wall and a rear wall of flexible material, the rear wall having an opening into the bag by which waste material can enter the bag and one of the walls has one or more vents through which gas may escape from the bag and having a filter covering said vent, said filter comprising an elongated, substantially flat filter body of a porous filter material interposed between gas and liquid impervious walls which are sealed to the body along its longitudinal side edges; gas inlet and outlet openings being provided in communication with the filter material adjacent to its respective longitudinal end regions, wherein both of the gas and liquid impervious walls are sealed to the upper and lower surfaces of the filter body, the arrangement being so that in use gas flows longitudinally through the filter from the inlet opening to the outlet opening, such gas flow being confined to said filter element, wherein the inlet opening is covered by a water impermeable sheet.
U.S. Pat. No. 5,342,434 discloses gas permeable materials being hydrophobic and oleophobic and the use of such materials for thereof in filters of medical vents where oil or fatty substances in parental drip bottles can clog gas vents. Furthermore, the use as a vent to vent air, water vapour, or other gases from an interior area, but yet due to the coating prevents oils from clogging the vents and to filter particulate impurities from an air stream in environments where presence of oils may tend to clog the pores of the material.
Thus, no method for avoiding wetting of the filter material caused by humidity or other liquid constituents of the visceral contents of an ostomy collection bag and at the same time preventing clogging of the filter has yet been proposed. Such liquids are not held back by hydrophobic surfaces and will cause wetting of the filter material which may lead to a blocking of the filter causing a build up of an undesirable pressure in the bag as mentioned above and may also lead to leakage and break-through of liquid through the filter which may cause a wetting of the patient's clothing and also to the liberation of unpleasant odours. Furthermore, there is still a need of measures for effectively preventing blocking of the inlet opening of filters of ostomy appliances and "pancaking" of ostomy appliances.
It has surprisingly been found that it is possible to reduce the risk of wetting of the filter material and at the same time to reduce the risk of blocking of the inlet opening of filters of ostomy appliances. Furthermore, it has been found that it may also be possible to overcome the problem of "pancaking" at the same time and to minimise the risk of flatus bypassing the filter.
It has surprisingly been found that the above drawbacks can be avoided if the inlet opening of the filter is covered with a microporous oleophobic membrane and a prefilter.